The present disclosure relates generally to electric power steering system and more particularly to narrow-frequency band feedback control of steering pinion torque associated therewith. It is to be appreciated, however, that the present disclosure may relate to other similar environments and applications.
In today's vehicles, electric power steering (EPS) is utilized to provide steering assistance based on particular vehicle dynamic conditions and maneuvers. In comparison with conventional hydraulic steering systems, an EPS system can provide safety enhancement by providing steering assistance during engine stall and ability to tune steering feel and performance. Further, an EPS system's electric motor is powered by the vehicle's alternator, instead of a hydraulic pump, which is belted into the engine. The efficiency advantage of an EPS system is derived from the fact that it is activated only when needed.
Development efforts have been made to gain favorable steering feel for various steering wheel input conditions in normal steering and handling areas which usually have a frequency range of steering input from zero to 2.5 Hz. External disturbance, which can be from an uneven or rough road surface, an unbalanced mass of tire or wheel, or break torque fluctuation, remains as a source to steering system which can cause unpleasant or annoying steering feel. Existing technologies utilize either a mechanical device to detect the source of steering torque or control logic to stabilize the torque sensor system to define bands of disturbance, which are used for motor current control. However, the frequency bands of common external disturbances to the steering system, such as steering shimmy caused by tire wheel unbalance, brake judder caused by breaking torque fluctuation, and kickback from uneven road surfaces, are much higher than normal steering and handling frequencies (e.g., greater than 2.5 Hz). Furthermore, these kinds of disturbances are all directly sensed by a steering pinion torque sensor and hence the steering signal. Conventional countermeasures to suppress such external disturbances are implemented via chassis sensitivity and receiver attenuation. However, simpler and more cost efficient approaches are desired.